The environmental conditions under which irradiation of polymeric devices and packaging films is conducted can significantly affect the properties of the polymer. Such irradiation of the polymers could be employed for sterilization, as is common in the medical and pharmaceutical industry, as well as for structural modification of polymer such as cross-linking. The presence of oxygen or air during irradiation may produce free radicals; radiation may also break bonds generating new reactive species such as HF, HCl, F−, Cl− from the polymer constituents. The effect of these radicals depends on the nature of the irradiated polymer, the presence of additives, and other parameters such as temperature, total dose, dose rate, and duration of the exposure of the reactive species. The term reactive species is used to indicate both the free radicals as well as other reactive species formed due to the effects of irradiation. These reactive species can cause chain scission reactions, in which the long backbone chains as well as side chains are cut, resulting in a loss of the molecular weight of the polymer along with changes to its structural properties. From a product use standpoint, the loss of desirable mechanical properties is one of the most important characteristics affected by irradiation of polymers. In the case of chlorofluoropolymers such as PCTFE used in packaging and barrier films, the release of byproducts such as low levels of HF, HCl and possibly other organic chlorofluorocarbons is also a matter of concern because they react with and have adverse effects on the barrier and structural properties of the packaging components as well as the packaged product itself.
To avoid oxidation, manufacturers generally avoid packaging components under atmospheric conditions, which was common practice in the past. An alternative is to package the component in foil, pull a vacuum on it or introduce a nitrogen/argon flush before irradiation sterilization. This eliminates most of the oxygen thereby reducing oxidation of the polymer during storage. Neither procedure completely solves the problem of reactive species generated by the effect of radiation on the polymers. These species can persist for years and react with the polymer and components thereof and packaged products during storage. This invention describes a process that reduces the oxidation and degradative reactions by scavenging the reactive species that are formed during irradiation and providing a relatively inert storage condition during post irradiation shelf life.